1. Field of the Invention
The present invention relates generally to electronic circuits, and more particularly to a flyback converter of simple structure and extremely high efficiency.
2. Description of the Related Art
U.S. Pat. No. 6,424,544 disclosed a continuous mode flyback converter, as shown in FIG. 6, in which, an FET (field-effect transistor) 71 provides a voltage drop for a secondary side of a transformer 72 to reduce loss of power energy, such that it is suitable for low voltage applications; besides, it further has DC-blocking CC to further reduce the loss of the power energy. The conventional converter prevents the gate voltage of the FET 71 from becoming zero and rapidly closes the FET 71 via a PNP transistor.
Japanese Publication No. 06-339266 disclosed a flyback converter using MOS transistor as synchronous rectifier, as shown in FIG. 7, in which a secondary side of a transformer 81 has an MOSFET 82 connected to a capacitor 83 and a resistor 84, a primary side of the transformer 81 works with a changeover drive circuit 85 and a diode 86, and a frequency control circuit 87 controls the frequency, such that the output can be controlled by conversion.